There are variety of methods of communicating over power lines known in the prior art. These prior art efforts to communicate across power lines range from simply applying a disturbance to a power line once per power cycle to communicating on a high frequency carrier on the power line. Although many of these communication schemes are functional, they suffer from a number of technical and economical drawbacks that make then unsuited for actual use. For example, U.S. Pat. No. 4,348,582 proposes the power line communication system depicted in the circuit in FIG. 1. To generate a notch 2 in the power signal 4 on the AC line 10, a silicon controlled rectifier 6 (SCR) controlled by a set of control circuitry 8 is gated for a short time, approximately 1 millisecond, before the AC voltage crosses zero from positive to negative. While the SCR 6 is conducting, the voltage applied to the load 12 remains near zero. This creates a notch 2 in the AC power signal 4 as shown in FIG. 2 that is being provided to a load 12. A receiver circuit in the load 12 detects the presence or absence of notches and interprets them as digital data.
There are several disadvantages to the above described approach. First, the transmission rate is only 60 bits per second since the notch can only be introduced on the positive to negative half cycle. The SCR cannot be turned off by its gate signal. Thus, if the SCR is turned on just after a zero crossing, the line will be shorted through the SCR for a half cycle of the power signal which in turn will open the fuse and immediately eliminate the circuit's ability to function.
Therefore, what is needed is a new and improved method of using AC power lines as a communication medium.
Electronic ballasts are typically low cost products that are produced and purchased in relatively large numbers. Therefore, it is also important that any power line communication system for use with electronic ballasts not dramatically increase the cost of the individual ballasts.